The present invention relates to the manufacture of light emitting diode (LED) lamps. The invention finds particular application in conjunction with the controlled application of a volume of a suspension media into a header cup supporting the diode.
The phosphor deposition process is a key step in the consistent fabrication of new miniature solid-state lamps from GaN based LED technology. The current dimensions of GaN LED""s die are (xcx9c300 micron) on a side, and are mounted in a shallow (xcx9c400 micron) header cup (xcx9c800 micron in diameter). Volumetrically, it only takes 500 nano-liter or less of phosphor carrier media, to fill the micro LED cups, in the lead-frame structures. This requires a phosphor deposition machine that is capable of dispensing phosphor media in volume smaller than 500 nano-liter with high precision. Since the light output from an LED lamp is highly sensitive to thickness variations in the deposited phosphor layer, small variations in the deposited volumes of phosphor materials, can cause dramatic differences in the color properties of the emitted light from the LED device.
Scanning electron microscope studies of commercially available LED lamps makes apparent that LED lamps are conventionally made in a multiple layered structure. Conventionally, an LED die is mounted to the header cup and covered with a layer of phosphor on the LED top surface, followed with a layer of silicone or epoxy overcoat.
The advantage of this method is that there exists more accurate liquid dispensing system for precise volume delivery of low viscosity suspensions. The disadvantage of this method is the lack of stability of the suspension towards sedimentation, resulting in premature settling of the phosphor particles prior to and during application (i.e., sedimentation stability).
In situations that require more than one layer to be used in suspension, additional difficulties arise such as segregation of different particles due to different densities, and new layer disruptions of the under layer by solvent action. In the situation that there is a phosphor particle size distribution, particle concentration gradients also may exist in the suspension. Both result in variations in the phosphor lay-down process, thus creating color variations.
The present invention contemplates an improved liquid dispensing system and method of manufacturing LEDs which overcomes the above-referenced problems and others.
In accordance with one embodiment of the present invention, a method of fabricating an LED lamp includes mounting an LED onto a platform and positioning a nano-liter pipette such that an interface separation is provided between the surface of the LED and the tip of the pipette. A single drop of phosphor dispersed suspension media is then dispensed from the Pipette over the surface of the LED and then cured.
In accordance with another aspect of the present invention, the dispensing step includes urging a determined volume of the suspension media from the pipette, such that the single drop physically contacts at least a portion of the surface of the LED and the tip of the pipette simultaneously.
In accordance with another embodiment of the present invention, a light emitting semiconductor device is formed by a process including positioning a source of color adjusting fluid such that an interface separation is provided between the surface of a semiconductor and the fluid source. A single drop of a color adjusting fluid is dispensed from the source onto the surface of the semiconductor and then cured.
In accordance with another aspect of the present invention, the fluid is cured by directing ultraviolet rays and/or thermal energy toward the fluid.
In accordance with another aspect of the present invention, the color adjusting fluid includes a silicone polymer blended with phosphor particles.
In accordance with another aspect of the present invention, a microscope is focused on the interface separation to achieve a separation of 1 mm between the source and the semiconductor surface.
In accordance with another embodiment of the present invention, a method of manufacturing an LED lamp includes dispersing particles throughout a suspension media, and blending the media to a defined viscosity. The suspension media is then deposited over an LED die and cured.
In accordance with another aspect of the present invention, the depositing step includes urging a drop defining a determined volume of the suspension media from the source such that the drop physically contacts at least a portion of the surface of the LED die before separating from the source.
In accordance with another aspect of the present invention, the dispersing step includes mixing phosphor particles having a diameter of less than 20 microns throughout the suspension media.
In accordance with another aspect of the present invention, the blending step includes forming the particle dispersed suspension media to a viscosity substantially between 1500 cP and 2500 cP.
One advantage of the present invention resides in the ability to control phosphor particle segregation through the suspension media.
Another advantage of the present invention resides in minimizing the number of laydown steps required to make the lamp.
Yet another advantage of the present invention resides in the reduced cost of manufacture of LED lamps.
A further advantage of the present invention resides in the narrowing the light spectral distribution of LED lamps manufactured under the present invention.
Still further advantages of the invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.